A level Biology: Post your doubts here!

[Yasmeen el-shaarawy]

Hey guys , I have a question regarding paper 41 may/June 2012. Can anyone explain part E in question 4? I tried really hard to understand the mark scheme but I didn't get a thing! :s anyways, any help would be much appreciated. Thanks!

 

[selena]

Which statement describes a process that occurs during protein synthesis?
A Transcription is the linking together of a tRNA molecule and a specific amino acid.
B Transcription is the linking together of free DNA nucleotides.
C Translation is the linking together of amino acids coded for by mRNA.
D Translation is the synthesis of an mRNA molecule by base pairing of nucleotides with DNA.

 

[selena]

A length of double-stranded DNA contains 120 nucleotides and codes for polypeptide X.
What is the maximum length of polypeptide X?
A 20 amino acids
B 40 amino acids
C 60 amino acids
D 120 amino acids

 

[selena]

http://papers.xtremepapers.com/CIE/...and AS Level/Biology (9700)/9700_w04_qp_1.pdf
can anyone please xplain q 19

 

[Amy Bloom]

Which statement describes a process that occurs during protein synthesis?
A Transcription is the linking together of a tRNA molecule and a specific amino acid.
B Transcription is the linking together of free DNA nucleotides.
C Translation is the linking together of amino acids coded for by mRNA.
D Translation is the synthesis of an mRNA molecule by base pairing of nucleotides with DNA.

I think its C. Linking of amino acids involves formation of polypeptides, the peptide link formation.

 

[littlecloud11]

A length of double-stranded DNA contains 120 nucleotides and codes for polypeptide X.
What is the maximum length of polypeptide X?
A 20 amino acids
B 40 amino acids
C 60 amino acids
D 120 amino acids

The answer will be A.
Double stranded DNA contains 120 nucleotides so a single strand would have 60 nucleotides. Each DNA strand acts as a template so the mRNA would also have 60 nucleotides. 3 nucleotides acts as a triplet and codes for a single amino acid. So the number of amino acids in the polypeptide would be 60/3 = 20

 

[strangerss]

Hey everyone , please I have a doubt in OCT/NOV 2012, 35 variant, I just don't get the answer , if 1 division on the stage micrometer is 0.1 and 1 eye piece graticule is 26 divisions then 26 multiplied by 0.1mm , to get the actual length of one eyepiece graticule right?? but I don't get how the answer is 0.004mm , please urgent help neeeded!

 

[HorsePower]

Hey everyone , please I have a doubt in OCT/NOV 2012, 35 variant, I just don't get the answer , if 1 division on the stage micrometer is 0.1 and 1 eye piece graticule is 26 divisions then 26 multiplied by 0.1mm , to get the actual length of one eyepiece graticule right?? but I don't get how the answer is 0.004mm , please urgent help neeeded!

in the figure, 1 stage micrometer div = 25 eye piece graticule divs (stage is the one which is larger)
and 1 stage micrometer div = 0.1 mm
therefore --- 0.1mm = 25 eye pice divs
so 1 eye piece div = 0.1/25 = 0.004mm

 

[aleezay]

The pitted walls of the xylem itself act as barrier, like the semi-permeable membrane does.

I dont think the walls are partially permeable. Lignin is totally impermeable, and pits would allow the passage of all substances (as far as i know).. Anyways, i think abcde is right

 

[selena]

What would be the result of analysing part of a DNA molecule?
A hexose sugars and phosphates in equal proportion, and an equal number of cytosine and
guanine bases
B nucleotides and phosphates in equal proportion, and an equal number of adenine and
cytosine bases
C pentose sugars and phosphates in equal proportion, and an equal number of adenine and
thymine bases
D twice as many phosphates as pentose sugars, and an equal number of adenine and guanine
bases

 

[PhyZac]

What would be the result of analysing part of a DNA molecule?
A hexose sugars and phosphates in equal proportion, and an equal number of cytosine and
guanine bases
B nucleotides and phosphates in equal proportion, and an equal number of adenine and
cytosine bases
C pentose sugars and phosphates in equal proportion, and an equal number of adenine and
thymine bases
D twice as many phosphates as pentose sugars, and an equal number of adenine and guanine
bases

answer is C

B and D are wrong since adenine isnt complementary to guanine or cytosine.
A is wrong since the sugar is pentose not hexose.

 

[daredevil]

I also have a question regarding respiration and oxygen debt. So when oxygen is not available, the pyruvate obtained from the glycolytic pathway does not enter the link reaction, right? Because of this, it is not combined with coenzyme A to form acetyl coenzyme A therefore the Krebs cycle will not start. So pyruvate will accept hydrogen to convert to lactate by the enzmye lactate dehydrogenase.

Some of this lactate will be oxidised when oxygen is available to CO2 and H2O. How will the rest of it from glycogen? Will it be converted to pyruvate and then to glucose and then to glycogen

ummm this is an A2 questions ryt?? AS mein to nahi hai na included??

 

[Amy Bloom]

I dont think the walls are partially permeable. Lignin is totally impermeable, and pits would allow the passage of all substances (as far as i know).. Anyways, i think abcde is right

I did not say, though that the lignified wall is semi-permeable, no. I just compared it as a barrier. TBH i'm a bit confused wid this.

 

[Thampi4]

Hi can someone list out the points why batch culture is used for penicillin production?

 

[gary221]

Hi can someone list out the points why batch culture is used for penicillin production?

bcoz penicillium doesnt make penicillin all the time. penicillin production only begins after the fungus has been growing in the medium for a while.
it is a secondary metabolite----> hence need to set up new fermentations.

 

[strangerss]

T

in the figure, 1 stage micrometer div = 25 eye piece graticule divs (stage is the one which is larger)
and 1 stage micrometer div = 0.1 mm
therefore --- 0.1mm = 25 eye pice divs
so 1 eye piece div = 0.1/25 = 0.004mm

Thanks due to my great brain powers I forgot that the eye piece graticule is with the smaller divisions -_-

 

[HorsePower]

^^ happens with me all the time

 

[Thampi4]

How does monoclonal antibodies help diagnostics better than traditional methods

 

[gary221]

How does monoclonal antibodies help diagnostics better than traditional methods

Monoclonal antibodies give a quicker diagnosis (than culturing pathogen) --> n hence a quicker treatment.
Also, identifying pathogens (viewing through) a microscope can be dificult
+ some pathogens/viruses cannot be cultured.

 

[daredevil]

heyy can anyone give me any notes or any other kind of guidance on plasma membrane .... esp the movement topics in it like facilitated diffusion, ATP wala transport, osmotic pressure and that stuf?? A star and syed1995